Members of Nigel Farage's political group in the European parliament have compared childbearing Muslim women to Osama bin Laden, spoken at a rally with the BNP's Nick Griffin, and defended some of the far-right views of the Norwegian mass murderer Anders Breivik.

Farage is facing a decision after the May elections over whether to keep Ukip in the Europe for Freedom and Democracy (EFD) group, an alliance of parties from different countries of which he is co-president, amid criticism of the extreme positions of some of its MEPs and examples of anti-Islam rhetoric on its website.

Ukip argues that all British political parties are forced to have "strange bedfellows" in Europe as it allows parties to qualify for more speaking time in the EU parliament. However, MEPs in any such alliance must have "political affinity" or risk being disbanded by the EU and losing their funding.

Some anti-Islam comments appear on the EFD's own website. In one video, Magdi Cristiano Allam, an MEP from the I Love Italy party, is translated as saying that Islam is not a religion but an ideology "that preaches hatred, violence and death, but that is something we're not allowed to say". His comments are made in response to a speaker at an EFD "study day", who argues against "caving in" to Muslims in Europe and warns of the threat of "Islamisation" of western society.

One politician in the EFD, Slavi Binev from Bulgaria, spoke at Ukip's conference last year. An interview with Binev on his website says: "If Osama bin Laden symbolises the cruellest aspect of the Islam for the Americans, then the Muslim woman with her numerous children are his European equivalent."

The group also contains Frank Vanhecke, a Belgian MEP, whose former party Vlaams Blok was disbanded after a court found it violated anti-racism legislation in 2002.

Vanhecke, now an independent, appeared at a student rally with Griffin, the BNP leader, in 2010 and told the Guardian he believes "Islamisation" is a serious problem for Europe.

Another politician in the group is Morten Messerschmidt, a Danish MEP whose youth organisation was given a conviction for incitement to racial hatred in 2002 after it argued crime such as rape was a product of a multi-ethnic society.

Ukip's biggest partners in the EFD group are the Italian Lega Nord, which is reportedly considering leaving the EFD after the May elections for a tie-up with Marine Le Pen's far-right French National Front. Farage's co-president is Francesco Speroni, an Italian MEP from Lega Nord, who defended some of the views of Breivik in 2011 saying: "If [Breivik's] ideas are that we are going towards Eurabia and those sorts of things, that western Christian civilisation needs to be defended, yes, I'm in agreement."

Earlier this year, one of the Italian anti-immigrant party's MPs, Gianluca Buonanno, "blacked up" in the country's parliament to make a point about the level of benefits for ethnic minorities.

Ukip said Lega Nord would be leaving the EFD alliance after the May elections, but Speroni told the Guardian last night that "any saying about this matter is very premature, nothing has been decided yet". He also said the EFD would have to check whether it has enough MEPs and member countries to remain "alive" under EU rules after the next election.

The rhetoric of some EFD parties contrasts with Farage's emphasis that Muslims are welcome in Ukip. The Ukip leader has said he will not go into an alliance with Geert Wilders, the anti-Islam Dutch politician, or the French Front National and publicly rejected the suggestion of Gerard Batten, a senior Ukip MEP, that Muslims should sign a code of conduct.

Arun Kundnani, an academic at New York University and author of The Muslims are Coming!, said it was worrying that a mainstream party such as Ukip has links to people who have expressed ideas of the Islamophobic far right.

"The argument that Islam is not a religion but a totalitarian ideology is the standard line of the US far-right Islamophobic conspiracy theorists," he said. "The term 'Islamisation' also has the same pedigree."

Mary Honeyball, a Labour MEP, added: "Ukip's decision to sit alongside such unsavoury groups as Lega Nord speaks volumes about where they really stand in relation to the extreme right."

Former Ukip MEP Mike Nattrass said the "undesirable" views of some EFD members was one reason he left the party. "All that to me is outrageous," he said. "Yes, [Farage] did need the numbers to make up the group," he said. "But [they] don't need these people. The problem in that group is they don't all really share the same views. Ukip isn't anti-Islam actually, though it might be in league with people who are."

Asked about his views, Vanhecke said he did speak at a Ghent rally "in company of Nick Griffin and MEPs from other rightwing parties" but he does not consider himself anti-Islam because he respects other cultures and would describe himself as a Flemish and European rightwing patriot.

"I do not remember if the theme was Islamisation (I rather think it was not) – but had it been so it would not have been a problem for me," he said. "I do consider Europe has a serious problem with Islamisation, a threat to fundamental democratic values such as the separation of church and state... and the strict egality between men and women."

Asked about his views on Muslims, as well as the conviction for racial hatred in 2002, Messerschmidt said: "The board of our youth movement, to which I belonged at that time, was convicted. The text was that a multi-ethnic society would lead to more crime, etc. There was no pointing in the text at specific groups, but a concern about the multi-ethnic ideology, something similar to what Cameron and Merkel have addressed."

A Ukip spokesman said: "The EFD group is a loose marriage of convenience formed in order to get more speaking time in the European parliament.

"Ukip is a libertarian party which condemns racism and xenophobia. The party does not share a common political platform with others involved in the EFD. All British political parties have strange bedfellows in the European Parliament. For example, the Labour Party participated in a Party of European Socialists (PES) summer camp in 2012 in which gay delegates were confronted with rampant homophobia and threatened with violence. Let Ed Miliband explain that."

The party said the speaker on Islam at an EFD study day was not an MEP, assistant or adviser to the EFD Group but merely giving a personal view from her experience.